It is desirable to provide a flexible coupling between the inboard engine and the outboard drive unit of a stern drive, particularly when the engine is mounted directly to the boat and the drive unit is mounted independently to the boat transom. In such installations, the natural flexibility of the boat as well as the required resilient engine mounts allow the limited degree of operational misalignment between the engine crankshaft and the input shaft of the drive unit. Prior stern drives have used resilient couplers such as that shown in U.S. Pat. No. 3,136,281 to Kiekhaefer, et al. While such couplers have been generally acceptable, under some conditions such as substantial angular misalignment under high power loadings, the rubber connections have failed.